The present invention relates to methods useful during sand control operations and, more particularly, to using water-soluble relative permeability modifiers that are useful for controlling fluid loss during sand control operations.
Hydrocarbon wells are often located in sections of subterranean formations that contain unconsolidated formation particulates that may migrate out of the subterranean formation with the oil, gas, water, and/or other fluids produced by the wells. The presence of formation particulates, such as formation sand, in produced fluids is undesirable in that the formation particulates may abrade pumping and other producing equipment and reduce the fluid production capabilities of the producing zones. As referred to herein, “unconsolidated formation particulates” include loose formation particulates and those wherein the bonded formation particulates cannot withstand the forces produced by the production of fluids therethrough.
Different techniques of controlling formation particulates have been developed and are commonly referred to as “sand control operations.” One common technique for performing a sand control operation is gravel packing. Gravel packing operations may be performed in horizontal, vertical, inclined, or otherwise formed portions of wells. Gravel packing operations typically use viscosified carrier fluids to suspend gravel particulates for delivery to a desired area in a well bore, e.g., near sections of a subterranean formation that contains unconsolidated formation particulates. In some horizontal wells, no viscosifying agents may be placed into the carrier fluid and high pumping rates may be used to deliver the gravel particulates to the desired location. Gravel particulates used during a gravel pack operation may be of a specific size designed to prevent the passage of formation particulates. One common type of gravel packing operation involves placing a gravel pack screen in the well bore and packing the annulus between the screen and the well bore with gravel particulates. Once in place, the gravel particulates act, inter alia, to prevent the formation particulates from occluding the screen or migrating with the produced fluids, and the screen acts, inter alia, to prevent the placed gravel particulates from entering the production tubing. After the gravel particulates have been placed in the desired location, the carrier fluid leaks off into the formation, inter alia, to allow the gravel particulates to settle into a gravel pack. Subsequently, the viscosity of the carrier fluid may be reduced (if needed), the well may be put back into production, and the carrier fluid may be produced back from the well. Other types of gravel packing operations may involve the use of gravel particulates coated with a resin or tackifying composition, wherein the gravel particulates may form hard, permeable masses therein to reduce the migration of formation particulates. In some instances, the processes of fracturing and gravel packing may be combined into a single treatment to provide a stimulated production and an annular gravel pack to prevent the migration of formation particulates. Such treatments are often referred to as “frac pack” operations.
A problem often encountered during sand control operations is excessive fluid loss into the formation. For example, during gravel pack operations and frac pack operations excessive fluid loss into the formation may cause a premature sandout to occur. As used herein, “premature sandout” refers to an undesired agglomeration of gravel particulates that can block the progress of the additional gravel particulates necessary to form the desired gravel pack. To prevent a premature sandout from occurring, fluid loss control additives commonly are included in the carrier fluids. Examples of commonly used fluid loss control additives include, but are not limited to, gelling agents, such as hydroxyethylcellulose and xanthan. Additional fluid loss control may be provided by crosslinking the gelling agent or by including sized solids in the carrier fluid, such as calcium carbonate.
A variety of service tools may be used during sand control operations, whereby removal of these service tools from the production packer after the sand control operation is necessitated. To prevent fluid loss into the formation during removal of these service tools, mechanical devices, such as flapper valves, may be used. In some instances, however, these mechanical devices may fail or otherwise cannot be used. In these instances, chemical fluid loss control pills may be used as supplements to the mechanical devices or as contingencies in case of their failure.
Conventional chemical fluid loss control pills may be characterized as either solids-containing pills or solids-free pills. Examples of solids-containing pills include sized-salt pills and sized-carbonate pills. These solids-containing pills often are not optimized for the particular downhole hardware and conditions that may be encountered. For instance, the particle sizes of the solids may not be optimized for particular gravel pack screen openings and, as a result, may invade into the interior of the gravel pack screen, which may greatly increase the difficulty of removal by subsequent remedial treatments. Additionally, high-solids loading in the pills, in conjunction with the large volumes of these pills needed to control fluid losses, may lead to the plugging of the interior and exterior of the gravel pack screen, which also may greatly increase the complexity of subsequent clean up. Furthermore, high loading of starches and biopolymers in the sized salt pills may add to the difficulty of cleanup either by flowback or remedial treatments. Solids-free fluid loss control pills commonly comprise crosslinked polymers that may not be effective without some invasion into the gravel pack screen and formation matrix. These pills typically require large volumes to control fluid loss and remedial treatments to remove.
Once fluid loss control may be no longer required, remedial treatments may be required to remove the previously placed pills, inter alia, so that the wells may be placed into production. For example, a chemical breaker, such as an acid, oxidizer, or enzyme may be used to either dissolve the solids or reduce the viscosity of the pill. In many instances, however, use of a chemical breaker to remove the pill from inside the screen may be either ineffective or not a viable economic option. Furthermore, the chemical breakers may be corrosive to the gravel pack screens and other downhole tools. Additionally, as the chemical breakers leak off into the formation, they may carry undissolved fines that may plug and/or damage the formation or may produce undesirable reactions with the formation matrix.